Many electrical devices are intolerant of application of DC voltage at a polarity opposite that which is normally applied to the device. Commonly, this opposite polarity condition may be referred to a reverse battery application though the opposite polarity voltage supply may actually originate from some source other than a battery or normal DC voltage supply. Protection from this condition is commonly referred to as reverse battery protection. Many devices will suffer irreversible damage from reverse battery application.
It is known to connect a diode between the negative terminal of a device and a DC supply negative terminal, the diode being oriented to block current flow through the device in reverse battery conditions by way of reverse bias blocking. Similarly, it is also known to connect a diode between the positive terminal of a device and a DC supply positive terminal, the diode being oriented to block current flow through the device in reverse battery conditions by way of reverse bias blocking. When operating with normal DC voltage polarity these arrangements suffer from intrinsic energy loss associated with the forward biased diode voltage drop. The actual DC voltage seen by the device is also reduced by the forward biased diode voltage drop.
It is also known to use a MOSFET driver between the positive terminal of a device and a DC supply positive terminal as a high side voltage switch and reverse battery protection. In this arrangement the device is generally wired to ground at the negative terminal, and when the driver is biased on the positive voltage is coupled to the positive terminal thereby coupling the device across the DC voltage at the normal polarity. The driver, when not biased on, provides reverse battery protection to the device. A major disadvantage to this arrangement is the necessity of a charge pump circuit to actively bias the driver conductive by ensuring the gate voltage exceeds the source voltage if the driver is an N-channel MOSFET. Substitution of a P-channel MOSFET, while eliminating the need for a charge pump to bias the driver conductive, may be impractical due to the increased size and cost of P-channel MOSFETs relative to N-channel MOSFETs. Additionally, P-channel MOSFETs are characterized by higher on resistances compared to N-channel MOSFETs which disadvantageously results in higher energy losses when biased conductive.